In one well-known architecture for an all-optical WDM network, each demand between an origin node and a destination node gets a dedicated wavelength channel that is unique on all of the links that make up the end-to-end path between that origin-destination node pair. Optical transport through such a network can be relatively simple, because cross-connection is carried out solely in the optical domain. However, the cost of network elements for such a network is relatively high, because wavelength channels are used inefficiently in general, and because network elements must be provided for relatively many wavelengths—roughly the square of the number of nodes of the network that are able to originate and receive transmissions.
In some cases, particularly in core networks, networks of this type may be economically viable if most of the wavelength channels are utilized to a substantial fraction of their full bandwidth capacities. However, it will often happen that the typical end-to-end demand fills only a small fraction of the total bandwidth available in a wavelength channel. In such cases, the economic viability of this type of network tends to suffer.
Various multiplexing techniques can be used to increase the utilization of specified wavelength channels on specified links of the network. In the technique known as traffic grooming, for example, disparate traffic streams routed through one or more common links are electronically multiplexed at their first common node and transported as an aggregate signal on a single wavelength channel. The aggregate signal is demultiplexed when a downstream common node is reached at or near which the streams diverge.
Although useful, traffic grooming tends to increase the equipment cost for the network, because it calls for optical-to-electronic conversion at the crossconnects, and the crossconnects will generally need relatively many inputs and outputs; i.e., they must have enough granularity to perform the necessary multiplexing and demultiplexing functions. Thus, the designer of a traffic-grooming network will generally be faced with a tradeoff between efficiency and cost.
Another approach for utilizing wavelength channels more efficiently is provided by optical burst switching (OBS). In OBS, optical signals are switched from input ports to output ports of an optical cross-connect on a per-burst basis. In other words, wavelengths are established between end-points only for a short duration and switched at intermediate nodes. One drawback of OBS is that in commercially viable networks, the optical signals will need to have switching times on the order of several microseconds or less. Little or no commercially available switching technology is able to achieve such speeds. Moreover, OBS does not scale well to large cross-connects.
Yet another disadvantage of known grooming approaches, generally, is that they involve additional network layers that increase the number of switching types and adaptation functions. As a consequence, these added functionalities tend to increase the overall network cost.
A new scheme for all-optical transmission on ring networks which overcomes some of the problems described above has been described in U.S. patent application Ser. No. 10/411,039, “Optical Network With Subwavelength Grooming,” cited above. However, there still remains a need to overcome the above problems in the context of a mesh network having at least one branch point.
In particular, then, there remains a need for a grooming approach in mesh networks having branch points that reduces the number of wavelength channels without electronic cross-connect, and that can be implemented with commercially available or emerging technology.